Warthin-Like Papillary Thyroid Carcinoma: Cytological Clues, Diagnostic Pitfalls and BRAFV600E Mutation Analysis

Warthin-like Papillary Thyroid Carcinoma (WL-PTC) is a rare subtype of PTC, frequently associated with Hashimoto thyroiditis. It is histologically distinct due to the presence of oncocytic follicular cells interspersed with dense lymphocytic infiltrate, resembling Warthin tumour of the salivary gland. This report adds to the limited literature by presenting three confirmed cases, highlighting the diagnostic challenges of WL-PTC on cytology and its potential to mimic benign inflammatory thyroid lesions and BRAFV600E mutation analysis.

All three patients presented with anterior neck swelling and were clinically euthyroid. FNAC smears showed moderately cellular aspirates with oncocytic cells, nuclear features of PTC (including grooves and pseudoinclusions), and a lymphoplasmacytic background, consistent with Bethesda Category VI. BRAFV600E mutation analysis performed by droplet digital PCR (ddPCR) was positive in two cases. Definitive diagnosis of WL-PTC was established on histopathology following thyroidectomy, with hallmark papillary structures lined by oncocytic cells and lymphoid-rich fibrovascular cores.

WL-PTC can closely mimic Hashimoto thyroiditis on cytology, posing a diagnostic challenge. Awareness of its cytological spectrum, mutation analysis and correlation with clinical and radiological findings is essential for accurate diagnosis and appropriate surgical management.